The use of titanium nitride films for making electrical connections is generally well known in the art and manufacture of integrated circuits. Titanium nitride has also been widely used in other diverse arts such as the production of wear resistant coatings on machine tools and as decorative coatings on watches and jewelry. Titanium nitride displays an interesting combination of properties, such as optical properties that resemble those of gold and a hardness greater than all elemental metals and sapphire and almost as hard as diamond. Its melting point is almost 3000.degree. C., which is higher than that of most materials, and it is inert to most chemicals and solvents except aqua regia, which dissolves it slowly, and hydrogen fluoride (HF). In addition, titanium nitride is a better electrical conductor than titanium metal.
Titanium nitride is currently being used for making electrical connections between upper level conductors and underlying substrate surfaces of silicon integrated circuits, and it is a preferred conductive material, for example, for making vertical electrical interconnects between a layer of surface conductor (e.g., metal or polysilicon) on a memory chip, such as a dynamic random access memory (DRAM), and an access transistor or stacked capacitor which is fabricated in or on the silicon substrate of the DRAM array. One such connection is shown, for example, in co-pending application Ser. No. 07/734,908 of Fernando Gonzalez et al filed on Jul. 24, 1991, assigned to the present assignee.
Present processes for forming these titanium nitride films include the reaction of either titanium tetrachloride, TiCl.sub.4, or a titanium-containing organic precursor in an LPCVD chamber with ammonia, NH.sub.3, to deposit the titanium nitride films. Such processes are generally well known in the art and are described, for example, in an article by R. M. Fix et al entitled "Synthesis of Thin Films by Atmospheric Pressure Chemical Vapor Deposition Using Amido and Imido Titanium (IV) Compounds as Precursors", Chemical Materials, Volume 2, No. 3, at pages 235-241, 1990, incorporated herein by reference.
Whereas these prior art titanium nitride film deposition processes have proven satisfactory in some respects, the conformality of these TiN films has been unacceptably low as a result of the highly reactive nature of the NH.sub.3 molecule and the fact that the NH.sub.3 molecule almost completely reacts with the titanium-containing reactant gas before it reaches the surface upon which it is desired to deposit a TiN film. This fact, in turn, causes the TiN compound to fall vertically downward in the reaction chamber being used and deposit out primarily on the horizontal receiving surfaces of IC structures being manufactured, but deposit very little TiN on the exposed vertical side walls of the IC structures, resulting in poor overall conformality of the deposited TiN coating.
Another disadvantage associated with the above NH.sub.3 type titanium nitride deposition process resides in the fact that the resistivity of the deposited titanium nitride films have in some cases been unacceptably high. Using these prior art TiN film producing processes, there is a strong tendency for the ratio of Ti to N in the TiN compound molecule to remain 1:1 regardless of variations introduced into conventional TiN film forming processes. A result of the high resistivity of the titanium nitride films thus produced is that it has the undesirable effect of limiting the amount of titanium silicide, TiSi.sub.2, which forms at the point that the TiN film makes contact with the silicon substrate. This fact, in turn, increases the contact resistance, Rc, within the integrated circuits being manufactured and thereby increases the heat dissipation and power losses therein.